There exist several concepts of testing methods detecting incorrectly connected contacts between off-chip antenna and on-chip antenna circuit. All these existing techniques have been developed for testing state of connection of electrical contacts. Electrical contacts are for example soldered contacts between off-chip antenna and on-chip antenna circuit. All these existing testing concepts present weaknesses.
According to one of these testing concepts, antenna circuit impedance is measured. A peak detector is used that is integrated in the power amplifier block of the transmitter. The peak voltage of the transmitted signal is measured on-chip. By measuring the peak voltage, the load impedance at the antenna circuit connection pads is calculated and verified against the specified range to check whether the antenna circuit is present or not, that is to say whether electrical contacts between off-chip antenna and on-chip antenna circuit are well soldered or not.
According to another one of these testing concepts, the transmitter output power is measured. The device is programmed to radiate a known output power, and then to measure with the spectrum analyzer this output power taking into account the over-the-air antenna to antenna loss. Here, the spectrum analyzer plays the role of a receiver. A measured output power below the programmed value means that there is a problem with the antenna circuit connection. This method needs extra equipments like a spectrum analyzer and its antenna.
According to another one of these testing concepts, either the signal or the signal to noise ratio, of the receiver is measured. A continuous wave signal is radiated to the antenna of the receiver. The resulting signal level and frequency offset are measured using an on-chip design for testability in the receiver circuit. A measured input power below the transmitted value, or a measured frequency offset higher than that specified by the design, means that the antenna circuit is not well connected. This method needs extra equipments like a radio frequency signal generator and its antenna.
According to another one of these concepts, a RX/TX loopback is used. As an example, let us take the case of an FM transceiver. The transmitter output is a frequency modulated single tone, with, for example, carrier frequency at 87.5 MHz. The antenna voltage is fed through a matched attenuator to the internal LNA input. At the output of the LNA, the signal strength is measured in the level detector block. The measured value is compared to a lower limit. In case the measured value is above the lower limit, this means that the antenna circuit connections are correct. If the measured value is below the lower limit, then the antenna connections are not correct. The bad quality factor caused by the absence of the antenna circuit attenuates the transmitted signal level. Hence, the lower received signal strength value.
Due to manufacturing needs, mobile phone manufacturers want to use mechanical structure where the antenna circuit, that is to say the antenna and its matching and filtering circuits, is connected to the phone with mechanical contacts instead of electrical contacts, for example spring contacts instead of soldering.
Badly connected antenna mechanical contact may cause a situation where the phone works somehow in a good network in big cities and poorly in the countryside where there is lower signal strength. This is very hard to detect using the production tests and Built-in Self-Test techniques known in prior art.
As well, this is very hard to detect in the service center where consumer walks in, because walk-in service centers are usually in good network coverage area and everything seems to be fine even when the antenna circuit is disconnected.